Relational Model Flashcards
When is the relational model created?
In the logical design stage.
What do the columns and rows define in a relation?
Col = Attributes, Rows = Instances (tuple)
What is the cardinality and degree of a relation?
Cardianlity = No. of instances in a relation, Degree = No. of attributes in a relation.
What are the 3 relational keys?
Primary Key, Foreign Key, Candidate Key.
What are the 2 main properties that a valid relation must follow?
No name clashes of attributes; Domain for attributes must be consistent; value names consistent.
Define a relational Database…
A relational database is a network of relations.
What is the difference between a relational schema and a relation instance?
Relational schema : The name and attributes that represent a relation. Relation Instance : A tuple of the relation.
What are the main constraints in relational models?
Integrity Constraints : Entity Integrity - Can’t be null
Referential Integrity - Foreign key must be primary key of its home relation
Domain Constraints - Set of allowable values that an attribute can take.
Define views…
Views are external sub schemas that can be customised for users.
Give some benefits of views…
Reduce complexity, improve security.
From where is data pulled to views?
View data is pulled from the base relation of the internal level.
What does it mean that data in the view is dynamic and derived?
View data is derived and dynamic. This means it can operate on the pulled data independently
of the internal level.
